Amid rising tensions over Georgia, U.S. officials are increasingly concerned that Russia is moving to rebuild one of the most dangerous features of the old Soviet Union’s security structure — its alliance with Cuba.

Moscow has been signaling that it wants to restore a long relationship with Havana that included not only economic ties, but also military and intelligence cooperation. The relationship brought the world to the brink of nuclear war during the Cuban missile crisis of 1962, when Russia secretly installed nuclear missiles on the island.

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U.S. officials believe that Russian statements are partly bluster, intended to dissuade the United States and its allies from moving the NATO alliance and military equipment, including missile defense sites, closer to the Russian border. And some experts question how interested Cuba is in rebuilding close ties with Russia.

But at a time when Russia has intervened forcefully in Georgia and is extending the global reach of its rebuilt military, some senior officials fear it may not be only bluster.

Russia “has strategic ties to Cuba again, or at least, that’s where they’re going,” a senior U.S. official said recently, speaking, like others, on condition of anonymity because of the sensitive implications of the assessments.